This invention relates generally to the docking of a floating test stage. More particularly, it relates to an apparatus for docking the test stage at a well-defined relative position between the test stage and a terrestrial base.
In the field of precision testing it is very important to isolate the sample from any external influences which interfere with the test and affect its results. The effects of external atmospheric influences are typically removed by placing the sample in an appropriate test chamber, e.g., a vacuum chamber. In these cases, the testing mechanism can be mounted in the chamber or external to it, depending on the types of measurements being performed.
In many cases, however, and especially in high precision measurements, the most detrimental external influences include mechanical disturbances such as jarring movements and vibrations. In the prior art, vibration isolation is commonly achieved by mounting the sample handling unit and testing apparatus on vibration isolated stages. In some fields, e.g., in optics where optical components are very sensitive to proper alignment and relative positioning, these components are mounted on optical benches with a hydraulic vibration isolation system. Such systems typically include one or more hydraulic cylinders or pneumatic cylinders. These types of benches are isolated from the base on which they are positioned, e.g., the floor. However, in the prior art system the sample can not be positioned precisely on the test stage, which is required for some precision measurements, since a loading state is not engaged with an appropriate vibration isolating mechanism.
There is a need, therefore, for an optical testing system with test stage docked to a loading stage at which the sample can be positioned precisely on the test stage.
Disadvantages associated with the prior art are overcome by a system for docking a floating test stage with integrated testing equipment at a predetermined position or docking position relative to a terrestrial base.
According to an exemplary embodiment, the system has a lift mechanism connected to the test stage and the base for docking the test stage to the docking position relative to the base. The system also includes a vibration isolation mechanism connected to the test stage for isolating the test stage from vibrations experienced by the base when floating over the base. The system also includes a first engaging mechanism connected to the vibration isolation mechanism for engaging with a second engaging mechanism positioned in the base. The first engaging means consists of a set of recesses, which can be flats, grooves, sockets and their combinations. The second engaging mechanism includes a set of projections, which may be balls, dimensioned to enter into the recesses in the first engaging mechanism. The second engaging mechanism is designed to engage and guide the test stage to a testing place. The first engaging mechanism may include three recesses oriented at substantially 120xc2x0 to each other, and the second engaging mechanism includes three corresponding projections.
Alternatively, the first engaging mechanism includes four recesses oriented at four corners of a rectangular, and the second engaging means includes four corresponding projections.
Alternatively, the second engaging mechanism can include a set of recesses, and the first engaging mechanism can include a set of projections.
The vibration isolation mechanism includes a set of shock absorbers, which can be hydraulic or pneumatic cylinders terminated with mechanical stages in which the recesses are machined. In addition, the shock absorbers can be either passive or active shock absorbers, and can be either in compression or tension. The lift mechanism also includes hydraulic or pneumatic cylinder and can simultaneously act as a shock absorber. The lift mechanism is mechanically decoupled from the base when the test stage is floating to achieve vibration isolation.
The system also includes a sample handling unit indexed to the docking position. The sample handling unit is used for loading and unloading samples, which are tested, on the test stage when the test stage is in docking position. The docking position is actually in a docking plane in three-dimensional space, and so the sample handling unit is indexed to that docking plane.
The system of the invention can be used in docking test stages used for optical testing of samples such as semiconductor wafers. In this case the testing equipment can include an optical source, e.g., a laser or some other light source. The equipment can also include an optical measurement unit, e.g., a photodetector or spectrometer for measuring the light reflected by the wafer. It is further advantageous that the test stage has a planar support mechanism for supporting planar samples. The test stage as well as the base can be enclosed in a test chamber, e.g., a vacuum chamber if desired.
Further details of the invention are set forth in the following detailed description with reference to the attached drawing figures.